Compression ignition (CI) engines may rely on multiple injections of fuel per combustion stroke for benefits such as reduced emissions and lowered combustion noise. Small variations in quantities of these injections may produce undesirable effects such as a substantial increase in emissions as well as noise, vibration, and harshness (NVH). Accordingly, injector flow may be continuously monitored and adapted so that a desired fuel quantity is accurately provided to the cylinders. In the example of new fuel injectors, flow characteristics may be learned on bench before the injectors are installed in an engine of a new vehicle. Additionally, these flow characteristics may be programmed into a controller of the vehicle to reduce the likelihood of increased emissions and NVH when operating the new vehicle.
The inventors herein have identified potential issues with the above approach. For example, a time to learn flow characteristics on bench for a pilot injection may not be adequate. In general, the desired offset to accurately deliver a quantity of the pilot injection may be learned only after driving at least 100-2000 miles under very specific driving conditions. Further, the engine assembly process may include labelling of fuel injectors with determined flow characteristics, marking of the engine label with the injector information, and calibration of the flow characteristics into the controller. These procedures can increase engine assembly times resulting in a significant increase in costs. Errors during labeling and programming may also occur during these procedures. Similar issues may also arise during vehicle service and maintenance. Furthermore, errors in calibrating the pilot injection may lead to shortened injector opening times, and in some cases, the pilot injection may be dropped altogether. These errors in pilot injection amounts and the longer durations needed for learning injection quantities can have adverse effects on cylinder pressure, emissions, and fuel economy, and may also increase NVH. Further still, while adaptation algorithms in a vehicle can learn and correct for errors in larger fuel quantities, inaccuracies in smaller pilot injections may need longer times to be corrected.
The inventors herein have recognized the above issues and have identified approaches to at least partially address them. In one example approach, a method for controlling a pilot injection is provided. The method comprises, during initial engine operation from vehicle manufacture, delivering a first proportion of fuel as a pilot injection, and only decreasing the first proportion of fuel responsive to learning of an injector flow characteristic. The first proportion of fuel delivered as the pilot injection may be a large enough quantity to ensure all injectors are injecting sufficient fuel. In this way, an engine may be operated such that fueling via the pilot injection may be assured.
For example, an engine in a newly manufactured vehicle may be operated with multiple injections per combustion cycle per cylinder wherein a first, larger predetermined proportion of fuel may be supplied as a pilot injection. The pilot injection may be followed by a main injection, which in turn may be followed by a post injection. A controller in the vehicle may monitor and learn flow characteristics of each fuel injector coupled to each cylinder in the engine. Further, the controller may learn the injector flow characteristics during different engine operating conditions such as idling, coast down, etc. Based on the learned injector flow characteristics, the first larger proportion of pilot injection may only be adjusted downward as initial engine operation continues. In one example, initial engine operation may be a given number of miles driven after initial vehicle manufacture. In another example, initial engine operation may include conditions when learned injector flow characteristics attain a stable value. Once initial engine operation is completed, adjustments to the pilot injection may be upward or downward.
In this way, a pilot injection may be assured to be a part of each multiple injection event. By commanding a predetermined larger proportion of pilot injection initially, a likelihood of omitting the pilot injection may be reduced. A controlled rate of air charge combustion may be maintained as injector flow characteristics for each new injector are learned and the pilot injection is adjusted downward. Further, the injector flow characteristics may be learned faster due to the initial larger setting which provides an initial higher gain. Additionally, by programming the larger proportion of initial pilot injection and learning desired pilot injection quantity during driving, on bench learning and encoding of an injector may be reduced enabling a decrease in injector production costs. Overall, benefits such as improved emissions compliance, reduced combustion noise, and cost savings may be attained.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.